Color cathode ray tube with a reduced dynamic focus voltage for an electrostatic quadrupole lens thereof

ABSTRACT

A color cathode ray tube has G 1 -G 5  electrodes and an anode. The G 5  electrode is divided into sub-electrodes supplied alternately with a first fixed focus voltage and a second focus voltage which is a second fixed voltage superposed with a dynamic voltage, at least one electrostatic quadrupole lens is formed between adjacent ones of the sub-electrodes, and two of the sub-electrodes are supplied with the second focus voltage. The following inequalities are satisfied: 0.0625×L (mm)≦B−20A/(3φ)≦22.0 mm, L (mm)≦352 mm, where A is an axial length of the G 4  electrode, φ (mm) is an average diameter of a center aperture in the G 4  electrode, B (mm) is a length from a cathode side end to a phosphor screen side end of said G 5  electrode to the phosphor screen.

[0001] This is a continuation of U.S. application Ser. No. 09/283,214,filed Apr. 1, 1999, the subject matter of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to a color cathode ray tube, andparticularly to a color cathode ray tube having a three beam in-line,dynamic focus type electron gun capable of providing good focuscharacteristics over the entire screen area and good display contrastwith a reduced dynamic focus voltage for its electrostatic quadrupolelens.

[0003] Color cathode ray tubes having an in-line type electron gun foruse in TV receivers or display monitors have a phosphor screen formed onthe inner surface of a faceplate of its panel portion, a shadow maskclosely spaced from the phosphor screen within the panel portion, adeflection yoke mounted around its funnel portion, and an in-line typeelectron gun housed in its neck portion. The in-line type electron gunincludes three cathodes arranged in line, and at least the first grid(G1) electrode, the second grid (G2) electrode, the third grid (G3)electrode and an anode, and projects three electron beams toward thephosphor screen.

[0004] To obtain good display image at the periphery of the phosphorscreen as well as the center of the phosphor screen, that is, uniformresolution over the entire phosphor screen by using a color cathode raytube having an in-line type electron gun, it is known to employ anelectron gun of the dynamic focus type in which an electrostaticquadrupole lens is formed between two adjacent ones among electrodes ofthe in-line type electron gun and one of the two is supplied with afixed focus voltage and the other of the two is supplied with-a fixedfocus voltage superposed with a dynamic voltage varying with deflectionof the electron beams.

[0005]FIG. 4 is a cross-sectional view of a prior color cathode ray tubeemploying an in-line type electron gun of the dynamic focus type(hereinafter referred to as a DF type in-line electron gun).

[0006] In FIG. 4, reference numeral 41 denotes a panel portion, 41F is afaceplate, 42 is a neck portion, 43 is a funnel portion, 44 is aphosphor screen, 45 is a shadow mask, 46 is an internal conductivecoating, 47 is a DF type in-line electron gun, 48 is a deflection yoke.

[0007] A grid electrode occupying the nth position counting from acathode is called a grid n electrode in this specification.

[0008] A grid occupying the nth position counting from a cathode iscalled a Gn in this specification.

[0009] In the DF type in-line electron gun 47, reference numerals 50 ₁,50 ₂ and 50 ₃ denote cathodes, 51 is a G1 electrode, 52 is a G2electrode, 53 is a G3 electrode, 54 is a G4 electrode, 55(1) is a firstG5 sub-electrode, 55(2) is a second G5 sub-electrode, 56 is a G6electrode (an anode), 57 is a shield cup, 58 are vertical electrodepieces, and 59 are horizontal electrode pieces.

[0010] The glass bulb of the color cathode ray tube comprises a panelportion 41, a neck portion 42 and a funnel portion 43. The panel portion41 is provided with the phosphor screen 44 coated on the inner surfaceof its faceplate 41F and the shadow mask 45 closely spaced from thephosphor screen 44 within the panel portion 41. The funnel portion 43 isprovided with the internal conductive coating 46 in its inner surfaceand the deflection yoke 48 mounted on the outer surface. The neckportion 42 houses the DF type in-line electron gun 47 therein.

[0011] The DF type in-line electron gun 47 comprises three cathodes 50₁, 50 ₂ and 50 ₃ arranged in line in a horizontal plane, and followingthe cathodes, the G1 electrode 51, the G2 electrode 52, the G3 electrode53, the G4 electrode 54, the first G5 sub-electrode 55(1), the second G5sub-electrode 55(2) the G6 electrode 56, the shield cup 57, arrangedalong the axis of the cathode ray tube in the order named. One centerand two side electron beam apertures in each of the G1 electrode 51, theG2 electrode 52, the G3 electrode 53, the G4 electrode 54, the first G5sub-electrode 55(1), the second G5 sub-electrode 55(2), the G6 electrode56, and the shield cup 57 are aligned with center lines O₂, O₁ and O₃ ofthe cathodes 50 ₂, 50 ₁ and 50 ₃, respectively.

[0012] In the G6 electrode 56, the center line of the center electronbeam aperture is aligned with the center line O₂ of the correspondingcathode 50 ₂, and the respective center lines of the two side electronbeam apertures are slightly displaced outwardly with respect to thecenter lines O₁ and O₃ of the corresponding cathodes 50 ₁ and 50 ₃,respectively. The first G5 sub-electrode 55(1) is provided with thevertical electrode pieces 58 sandwiching horizontally each of the threeelectron beam apertures in its end facing the second G5 sub-electrode55(2), and the second G5 sub-electrode 55(2) is provided with a pair ofthe horizontal electrode-pieces 59 sandwiching vertically the threeelectron beam apertures in common in its end facing the first G5sub-electrode 55(1). The vertical electrode pieces 58 and the horizontalelectrode-pieces 59 form an electrostatic quadrupole lens between thefirst and second G5 sub-electrodes 55(1), 55(2).

[0013] In operation, the first G5 sub-electrode 55(1) is supplied with afixed-focus voltage, the second G5 sub-electrode 55(2) is supplied witha fixed focus voltage superposed with a dynamic voltage varying withdeflection of the electron beams, and the G6 electrode 56 serving as ananode, the shield cup 57 and the internal conductive coating 46 aresupplied with an accelerating voltage (an anode voltage).

[0014] In the prior art color cathode ray tube, three electron beamsemitted from the three cathodes 50 ₁, 50 ₂, 50 ₃ of the DF type in-lineelectron gun 47 travel accelerated and focused along the respectivecenter lines O₁, O₂, O₃ through the electron beam apertures in each ofthe G1 electrode 51, the G2 electrode 52, the G3 electrode 53, the G4grid electrode 54, the first G5 sub-electrode 55(1), the second G5sub-electrode 55(2), the G6 electrode 56, the shield cup 57, and areprojected from the electron gun 47 toward the phosphor screen 44. Thethree electron beams projected from the electron gun 47 are properlydeflected horizontally and vertically by the deflection yoke 48, thenpass through an electron beam aperture in the shadow mask 45 and impingeupon the phosphor screen 44 to produce a desired image on the phosphorscreen 44.

[0015] Color cathode ray tubes for use in color display monitors and thelike usually employ a self-converging deflection yoke 48 of the typehaving both horizontal and vertical deflection windings wound in asaddle configuration (hereinafter referred to as the saddle/saddle type)to prevent magnetic fields generated by the deflection yoke 48 fromradiating from the monitor to its outside.

[0016] The self-converging deflection yoke 48 increases deflectiondefocusing on the phosphor screen 44 due to the inherent non-uniformityin its deflection magnetic fields, deteriorates image resolution at theperiphery of the phosphor screen 44 and therefore an electrostaticquadrupole lens is employed in the in-line type electron gun 47 with adynamic focus voltage varying with deflection of the electron beams.

[0017] When the deflection of the electron beams is zero or very small,that is, when the electron beams scan the central portion of thephosphor screen 44, a dynamic voltage becomes zero or very small, afocus voltage applied to the first G5 sub-electrode 55(1) becomes equalor nearly equal to a focus voltage applied to the second G5sub-electrode 55(2), the strength of the electrostatic quadrupole lensis weakened and consequently no astigmatism is produced in the electronbeam spot at the center of the phosphor screen 44.

[0018] When the deflection of the electron beams is large, that is, whenthe electron beams scan the periphery of the phosphor screen 44, thedynamic voltage becomes large, the focus voltage applied to the secondG5 sub-electrode 55(2) becomes higher than the focus voltage applied tothe first G5 sub-electrode 55(1) and the strength of the electrostaticquadrupole lens becomes stronger to produce astigmatism of the electronbeams deflected to the periphery of the phosphor screen 44. Thisastigmatism causes the shape of the beam spot on the phosphor screen toelongate its core portion vertically and to elongate its halohorizontally such that deflection defocusing caused by theself-converging deflection yoke 48 is canceled out and resolution at theperiphery of the phosphor screen 44 is improved.

[0019] In a color cathode ray tube employing the prior art DF typein-line electron gun, a distance between its main lens and the peripheryof the phosphor screen 44 is longer than that between its main lens andthe center of the phosphor screen 44, and the electron beam focusingcondition for the center of the phosphor screen 44 differs from that forthe periphery of the phosphor screen 44 such that adjustment for thebest beam focus at the center of the phosphor screen 44 degrades thebeam focus and resolution at the periphery of the phosphor screen 44. Ifa correction lens for curvature of the image field is incorporated inthe DF type in-line electron gun 47, when the electron beams aredeflected to the periphery of the phosphor screen 44, a focus voltageapplied to the second G5 sub-electrode 55(2) becomes higher, adifference between the focus voltage and an accelerating voltage, (ananode voltage) applied to the G6 electrode 56 decreases and the strengthof the focus lens weakens such that the focus point (the image point) ofthe electron beams is moved toward the phosphor screen 44, the electronbeams deflected to the periphery of the screen 44 are focused on thephosphor screen 44 and deterioration in resolution at the periphery ofthe screen 44 is prevented. In this way, by using a dynamic voltage, theprior color cathode ray tube can correct curvature of the image field aswell as astigmatism in electron beam spots.

[0020] The prior art color cathode ray tube corrects astigmatism in beamspot and curvature of the image field by applying a dynamic voltage tothe second G5 sub-electrode 55(2) of an electrostatic quadrupole lens.If a color cathode ray tube for use in a color monitor or the likeemploys a deflection yoke 48, of a relatively wide deflection angle, 95°to 105°, for example, to reduce the depth of the monitor, a requireddynamic voltage becomes a little too high for a color monitor due to itslarge deflection angle of the electron beams, and a distance between themain lens and the phosphor screen (hereinafter referred to as alens-screen distance) becomes shorter such that the scanning electronbeams and electron beam apertures in the shadow mask 45 interfere witheach other and produce raster moire (horizontal spurious stripes) on thephosphor screen.

[0021] To solve the above problems in the DF type in-line electron gun,the present inventors previously proposed an electron gun satisfying thefollowing inequalities to reduce the magnitude of a dynamic voltage andreduce appearance of raster moire (horizontal spurious stripes) on thephosphor screen:

[0022] 0.06×L (mm)≦B−20×A/(3φ)≦19.0 (mm), and L≦352 (mm)

[0023] where

[0024]  A (mm) is an axial length of the G4 electrode,

[0025]  φ (mm) is a diameter of an aperture in the G4 electrode,

[0026]  B (mm) is an axial length of the G5 electrode, and

[0027]  L (mm) is a distance between the end of the G5 electrode on itsphosphor side and the phosphor screen.

[0028] When the proposed color cathode ray tube employs a dark taintedpanel (light transmission of 38%, for example) for a faceplate of apanel portion to increase its display contrast ratio and it is operatedto provide the display brightness equal to that of a color cathode raytube employing a tainted panel (light transmission of 50%, for example),there arises a new problem that electron beam spots on the phosphorscreen are enlarged.

[0029] For example, if the proposed color cathode ray tube employs afaceplate with its light transmission reduced by about 20% compared withthat of a tainted panel by using a dark-tainted panel and by applyingantistatic and antireflection coating on the dark-tainted panel ifnecessary, a beam current for each cathode has to be increased by about30% to obtain a brightness equivalent to that of a color cathode raytube employing the tainted panel and consequently its beam spot diameteris increased by about 10%.

SUMMARY OF THE INVENTION

[0030] The present invention solves the above problems, it is an objectof the present invention to provide a color cathode ray tube capable ofcorrecting astigmatism of electron beam spots and curvature of the imagefield, reducing the magnitude of a dynamic voltage even when it employsa wide-angle deflection yoke and reducing appearance of raster moire onthe phosphor screen.

[0031] To accomplish the above object, in accordance with one embodimentof the present invention, there is provided a color cathode ray tubecomprising an evacuated envelope comprising a panel portion, a neckportion, a funnel portion for connecting the panel portion and the neckportion, a phosphor screen formed on an inner surface of a faceplate ofthe panel portion, an in-line type electron gun housed in the neckportion and a deflection yoke mounted around the funnel portion; thein-line type electron gun comprising an electron beam generating sectionhaving three in-line cathodes, a G1 electrode and a G2 electrodearranged in the order named for projecting three electron beams arrangedapproximately in parallel with each other in a horizontal plane towardthe phosphor screen, and an electron beam focusing section comprising aG3 electrode, a G4 electrode, a G5 electrode and an anode arranged inthe order named for focusing the three electron beams on the phosphorscreen, wherein the G5 electrode comprises a plurality of sub-electrodesarranged to be supplied alternately with a first focus voltage and asecond focus voltage, the first focus voltage being a first fixedvoltage, the second focus voltage being a second fixed voltagesuperposed with a dynamic voltage varying with deflection of the threeelectron beams, at least one electrostatic quadrupole lens is formedbetween two of the plurality of sub-electrodes supplied alternately withthe first focus voltage and the second focus voltage, two of theplurality of sub-electrodes are supplied with the second focus voltage,the G4 electrode, the G5 electrode and the phosphor screen satisfyfollowing inequalities: 0.0625×L (mm)≦B−20A/(3φ)≦22.0 mm, L (mm)≦352 mm,where A (mm) is an axial length of the G4 electrode, φ (mm) is anaverage of horizontal and vertical diameters of an electron beamaperture for a center electron beam of the three electron beams in theG4 electrode, B (mm) is an axial length measured from a cathode side endof the G5 electrode to a phosphor screen side end of the G5 electrode,and L (mm) is an axial distance from the phosphor screen side end of theG5 electrode to a center of the phosphor screen.

[0032] To accomplish the above object, in accordance with anotherembodiment of the present invention, there is provided a color cathoderay tube comprising an evacuated envelope comprising a panel portion, aneck portion, a funnel portion for connecting the panel portion and theneck portion, a phosphor screen formed on an inner surface of afaceplate of the panel portion, an in-line type electron gun housed inthe neck portion, and a deflection yoke mounted around the funnelportion; the in-line type electron gun comprising an electron beamgenerating section having three in-line cathodes, a G1 electrode and aG2 electrode arranged in the order named for projecting three electronbeams arranged approximately in parallel with each other in a horizontalplane toward the phosphor screen, and an electron beam focusing sectioncomprising a G3 electrode, and an anode arranged in the order named forfocusing the three electron beams on the phosphor screen, wherein the G3electrode comprises a plurality of sub-electrodes arranged to besupplied alternately with a first focus voltage and a second focusvoltage, the first focus voltage being a first fixed voltage, the secondfocus voltage being a second fixed voltage superposed with a dynamicvoltage varying with deflection of the three electron beams, at leastone electrostatic quadrupole lens is formed between two of the pluralityof sub-electrodes supplied alternately with the first focus voltage andthe second focus voltage, two of the plurality of sub-electrodes aresupplied with the second focus voltage, the G3 electrode and thephosphor screen satisfy following inequalities: 0.0625×LA (mm)≦C≦22.0mm, LA (mm)≦352 mm, where C (mm) is an axial length measured from acathode side end of the G3 electrode to a phosphor screen side end ofthe G3 electrode, and LA (mm) is an axial distance from the phosphorscreen side end of the G3 electrode to a center of the phosphor screen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In the accompanying drawings, in which like reference numeralsdesignate similar components throughout the figures, and in which:

[0034]FIG. 1 is a horizontal cross-sectional view of a first embodimentof a color cathode ray tube in accordance with the present invention.

[0035]FIG. 2A is a graph showing a relationship between axial lengths ofan electrode and dynamic voltages in a DF type in-line electron gun, andFIG. 2B is a graph showing a relationship between axial lengths of theelectrode and electron beam spots in the DF type in-line electron gun.

[0036]FIG. 3 is a horizontal cross-sectional view of a second embodimentof a color cathode ray tube in accordance with the present invention.

[0037]FIG. 4 is a horizontal cross-sectional view of a color cathode raytube employing a prior art dynamic focus type in-line electron gun.

[0038]FIG. 5 is a cross-sectional view of a second G5 sub-electrode ofFIG. 1 as viewed in the direction of arrows V-V in FIG. 1.

[0039]FIG. 6 is a cross-sectional view of a third G5 sub-electrode ofFIG. 1 as viewed in the direction of arrows VI-VI in FIG. 1;

[0040]FIG. 7 is a vertical cross-sectional view of a third embodiment ofa color cathode ray tube in accordance with the present invention.

[0041]FIG. 8 is a vertical cross-sectional view of a fourth embodimentof a color cathode ray tube in accordance with the present invention.

[0042]FIG. 9 is a cross-sectional view of a second G5 sub-electrode ofFIG. 7 as viewed in the direction of arrows IX-IX in FIG. 7.

[0043]FIG. 10 is a cross-sectional view of a third G5 sub-electrode ofFIG. 7 as viewed in the direction of arrows X-X in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The present invention will now be described in detail withreference to the accompanying drawings.

[0045]FIG. 1 is a horizontal cross-sectional view of a first embodimentof a color cathode ray tube in accordance with the present invention.

[0046] In FIG. 1, reference numeral 1 denotes a panel portion, 1F is afaceplate of the panel portion 1, 2 is a neck portion, 3 is a funnelportion, 4 is a phosphor screen, 5 is a shadow mask, 6 is an internalconductive coating, 7 is a DF type in-line electron gun, and 8 is aso-called saddle-saddle type deflection yoke having horizontal andvertical deflection windings wound in a saddle configuration for amaximum diagonal deflection angle of 100°.

[0047] In the DF type in-line electron gun 7, reference numeral 10 ₁denotes a left-hand cathode, 10 ₂ is a center cathode, 10 ₃ is aright-hand cathode, 11 is the G1 electrode, 12 is the G2 electrode, 13is the G3 electrode, 14 is the G4 electrode, 15(1) is a first G5sub-electrode, 15(2) is a second G5 sub-electrode, 15(3) is a third G5sub-electrode, 16 is the G6 electrode, 17 is a shield cup, 18 arevertical electrode pieces and 19 are horizontal electrode pieces. Onesub-electrode may be comprised of one or more members.

[0048] The glass bulb of the color cathode ray tube comprises a panelportion 1 having a faceplate 1F, a small-diameter neck portion 2 and agenerally frustum-shaped funnel portion 3 for connecting the panelportion 1 and the neck portion 2. A phosphor screen 4 is coated on theinner surface of the faceplate 1F and a shadow mash 5 is closely spacedfrom the phosphor screen 4 within the panel portion 1. An internalconductive coating 6 is coated on the inner surface of the funnelportion 3, a deflection yoke 8 is mounted around the funnel portion 3,and the DF type in-line electron gun 7 is housed in the neck portion 2.

[0049] The DF type in-line electron gun 7 comprises the left-handcathode 10 ₁, the center cathode 10 ₂ and right-hand cathode 10 ₃arranged in line in a horizontal plane, and following the cathodes, theG1 electrode 11, the G2 electrode 12, the G3 electrode 13, the first G5sub-electrode 15(1), the second G5 sub-electrode 15(2), the third G5sub-electrode 15(3), the fourth G5 sub-electrode 15(4), the G6 electrode16, the shield cup17, arranged along the axis of the cathode ray tube inthe order named. Center lines of a left-hand beam aperture, a centerbeam aperture and a right-hand beam aperture in each of the G1 electrode11, the G2 electrode 12, the G3 electrode 13, the G4 electrode 14, thefirst G5 sub-electrode 15(1), the second G5 sub-electrode 15(2), thethird G5 sub-electrode 15(3), the phosphor-side end of the G6 electrode16, and the shield cup 17 are aligned with center lines O₁, O₂ and O₃ ofthe cathodes 10 ₁, 10 ₂ and 10 ₃, respectively.

[0050] In the cathode-side end of the G6 electrode 16, the center lineof the center electron beam aperture is aligned with the center line O₂of the center cathode 10 ₂, and the center line of the left-handelectron beam aperture is slightly displaced outwardly with respect tothe center line O₁ of the left-hand cathodes 10 ₁ and the center line ofthe right-hand electron beam aperture is slightly displaced outwardlywith respect to the center line O₃ of the right-hand cathodes 10 ₃.

[0051] The following explains the structure of electrodes for formingthe electrostatic quadrupole lens formed between the second G5sub-electrode 15(2) and the third G5 sub-electrode 15(3).

[0052]FIG. 5 is a cross-sectional view of the second G5 sub-electrode15(2) of FIG. 1 as viewed in the direction of arrows V-V in FIG. 1, andFIG. 6 is a cross-sectional view of the third G5 sub-electrode 15(3) ofFIG. 1 as viewed in the direction of arrows VI-VI in FIG. 1.

[0053] The second G5 sub-electrode 15(2) is provided with the verticalelectrode pieces 18 sandwiching horizontally each of the three electronbeam apertures 152 a, 152 b, 152 c in its end facing the third G5sub-electrode 15(3), and the third G5 sub-electrode 15(3) is providedwith a pair of the horizontal electrode pieces 19 sandwiching verticallythe three electron beam apertures 153 a, 153 b, 153 c in common in itsend facing the second G5 sub-electrode 15(2). The vertical electrodepieces 18 and the horizontal electrode pieces 19 form an electrostaticquadrupole lens between the second and third G5 sub-electrodes 15(2),15(3).

[0054] In FIGS. 5 and 6, the reference numerals 18 a and 19 a denotebaseplates for welding the vertical and horizontal electrode pieces tothe second and third sub-electrodes, respectively.

[0055] The G1 electrode 11 is supplied with a voltage approximatelyequal to or near zero volt, the G2 electrode 12 and the G4 electrode 14are supplied with a relatively low voltage Vg2 of about 400 to about1000 volts, the G3 electrode 13 and the second G5 sub-electrode 15(2)are supplied with a fixed voltage Vfs of about 5 kV to about 10 kV, thefirst G5 sub-electrode 15(1) and the third G5 sub-electrode 15(3) aresupplied with a focus voltage (Vfd+dVf) which is a fixed voltage Vfdsuperposed with a dynamic voltage dVf varying with deflection of theelectron beams, and the G6 electrode 16, the shield cup 17 and theinternal conductive coating 6 are supplied with an accelerating voltage(an anode voltage) Eb of about 20 kV to about 30 kV. Here the followingrelationship is satisfied:

Vfs≧Vfd+dVf.

[0056] The color cathode ray tube of the first embodiment operates asfollows:

[0057] Three electron beams emitted from the three cathodes 10 ₁, 10 ₂,10 ₃ of the DF type in-line electron gun 7 travel accelerated andfocused along the respective center lines O₁ O₂, O₃ of the threecathodes through the electron beam apertures in each of the G1 electrode11, the G2 electrode 12, the G3 electrode 13, the G4 electrode 14, thefirst, second and third G5 sub-electrodes 15(1), 15(2), 15(3), the G6electrode 16 and the shield cup 17, and they are projected from theelectron gun 47 toward the phosphor screen 4. The three electron beamsprojected from the electron gun 7 are properly deflected horizontallyand vertically by the deflection yoke 18, then pass through an electronbeam aperture in the shadow mask 5 and impinge upon the phosphor screen4 to produce a desired image on the phosphor screen 4.

[0058] The vertical electrodes 18 attached to the second G5sub-electrode 15(2) and the horizontal electrode pieces 19 attached tothe third G5 sub-electrode 15(3) form an electrostatic quadrupole lenstherebetween, and the third G5 sub-electrode 15(3) is supplied with thefocus voltage (Vfd+ dVf) containing the dynamic voltage dVf varying withdeflection of the electron beams.

[0059] When the electron beams scan the central portion of the phosphorscreen 4 with their deflection being zero or very small, the dynamicvoltage dVf is zero or a very small positive value, and the focusvoltage (Vfd+dVf) applied to the third G5 sub-electrode 15(3) is set tobe lower than the focus voltage Vfs applied to the second G5sub-electrode 15(2).

[0060] When the electron beams scan the periphery of the phosphor screen4 with their deflection being large, the dynamic-voltage is large, thefocus voltage (Vfd+dVf) applied to the third G5 sub-electrode 15(3)approaches the focus voltage Vfs applied to the second G5 sub-electrode15(2) and the electrostatic quadrupole lens functions to compresselectron beam spots in a horizontal direction and to expand the electronbeam spots in a vertical direction, at the periphery of phosphor screen4. The astigmatism produced on the beam spot elongates its core portionvertically and elongates its halo horizontally such that it cancels outdeflection defocusing caused by the self-converging deflection yoke 8and it improves resolution at the periphery of the phosphor screen 4.

[0061] The above-mentioned deflection defocusing can be eliminated orreduced more effectively by making a main lens formed between the thirdG5 sub-electrode 15(3) and the G6 electrode 16 such that electron beamsare focused more strongly in a horizontal direction than in a verticaldirection. The deflection defocusing can also be eliminated or reducedeffectively by forming a lens for focusing electron beams more stronglyin a horizontal direction than in a vertical direction in a spacebetween the G3 electrode 13 and the first G5 sub-electrode 15(1), orbetween the G2 electrode 12 and the G3 electrode 13.

[0062] In the electrostatic quadrupole lens of the DF type in-lineelectron gun 7 in which the first and third G5 sub-electrodes 15(1),15(3) are supplied with the focus voltage (Vfd+dVf) containing thedynamic voltage dVf, when the electron beam scans the periphery of thephosphor screen 4, the focus voltage (Vfd+dVf) applied to the first andthird G5 sub-electrode 15(1), 15(3) becomes higher, a difference betweenthe focus voltage (Vfd+dVf) and the focus voltage Vfs applied to thesecond G5 sub-electrode 15(2) and a difference between the focus voltage(Vfd+dVf and the accelerating voltage Eb applied to the G6 electrode 16decrease and the strength of the lens formed between the first andsecond G5 sub-electrodes 15(1), 15(2) and the strength of the main lensformed between the third G5 sub-electrode 15(3) and the G6 electrode 16decrease. As a result, the electron beam focus point (the image point)is moved toward the phosphor screen 4 such that the electron beamdeflected to the periphery of the screen 4 is focused on the phosphorscreen 4 and deterioration in resolution is prevented at the peripheryof the phosphor screen 4.

[0063] In this way, the color cathode ray tube employing the DF typein-line electron gun 7 of the first embodiment forms twocurvature-of-the-image-field correction lenses between the first andsecond G5 sub-electrodes 15(1), 15(2) and between the third G5sub-electrode 15(3) and the G6 electrode 16, and one electrostaticquadrupole lens between the second and third G5 sub-electrodes 15(2),15(3) by applying the focus voltage (Vfd+dVf) containing the dynamicvoltage dVf to the first and third G5 sub-electrodes 15(1), 15(3), andcorrects astigmatism of an electron beam spot and curvature of the imagefield.

[0064]FIGS. 2A and 2B are graphs showing a relationship between thedynamic voltages dVf and the lengths of the final focus electrodeadjacent to the anode and that between the diameter of the beam spotsand the lengths of the final focus electrode in the DF type in-lineelectron gun, respectively,

[0065]FIG. 2A showing a relationship between axial lengths of the finalfocus electrode and dynamic voltages dvf and FIG. 2B showing arelationship between axial lengths of the final focus electrode and thediameter of electron beam spots.

[0066] The final focus electrode comprises three or more sub-electrodessupplied with one or more relatively high voltages.

[0067] In FIG. 2A, the dynamic voltages dvf are plotted as ordinates andthe effective lengths of the final focus electrode as abscissas.

[0068] The effective length of the final focus electrode of the DF typein-line electron gun is defined as {B−20A/(3φ)} in FIG. 1, where B is anaxial length a cathode-side end of the first G5 sub-electrode 15(1) to aphosphor-screen-side end of the fourth G5 sub-electrode 15(4), A is anaxial length of the G4 electrode 14, φ is a diameter of an electron beamaperture for the center electron beam in the G4 electrode 14 and is anaverage of horizontal and vertical diameters of the center electron beamaperture in the G4 electrode if the center electron beam aperture isnon-circular, such as elliptical, oval or rectangular.

[0069] As numerical examples, the axial length A of the G4 electrode isabout, 0.5 mm to about 1.0 mm, and the diameter φ of the electron beamaperture in the G4 electrode is about 4 mm.

[0070] The correction term 20A/(3φ) represents the effect of theelectron beam aperture in the G4 electrode 14 and a factor 20/3 isdetermined by experiment.

[0071] Line “a” indicates characteristics of a color cathode ray tube ofthe first embodiment using a 1000 deflection yoke 8 and line “b”indicates characteristics of a color cathode ray tube with a 1000deflection yoke, previously proposed by the present inventors.

[0072] A lens-screen distance L is defined as a distance from the centerof a phosphor screen to the anode-side end of a focus electrode forforming a final stage of a main lens in cooperation with the anode.

[0073] In FIG. 2B, the ordinates represent the diameters of the electronbeam spots on the phosphor screen at the standard electron beam currentand the abscissas represent the effective lengths of the final focuselectrodes normalized by the lens-screen distance.

[0074] Line “a” indicates characteristics of a color cathode ray tubeemploying a dark-tainted panel (light transmission approximately 38%)serving as a faceplate 1F of the panel portion, of the first embodiment,and line “b” indicates characteristics of a color cathode ray tubepreviously es proposed by the present inventors and employing a taintedpanel (light transmission approximately 50%) serving as a faceplate.

[0075] The standard electron beam currents provide recommendedbrightness for respective screen sizes and are defined as 0.00115(μA/mm²)×D(mm)², D being a useful diagonal dimension of the phosphorscreen. As specific examples, the approximate standard electron beamcurrents are 200 μA, 250 μA, and 300 μA for useful diagonal screendimensions D of 41 cm, 46 cm, and 51 cm, respectively.

[0076]FIG. 2A shows that, in a color cathode ray tube employing the DFtype in-line electron gun, the dynamic voltages dvf is reduced withdecrease in the effective length of the final focus electrode.

[0077] A relatively large screen size is more suited to ahigh-definition display monitor for use in graphic terminals or the likecapable of displaying a high-resolution image of drawings as well asletters or characters than a small size screen used in personalcomputers are. But considering the desire to make a space occupied by amonitor as small as possible, as a measure to reduce the depth of themonitor, there is a tendency to reduce the axial length of a colorcathode ray tube by increasing the deflection angle of electron beams inthe color cathode ray tube. The increase of the deflection anglerequires the increase in the magnitude of the above-explained dynamicvoltage.

[0078] In the operation of the color cathode ray tube in the highdefinition display monitor, the frequency of the dynamic voltage is madehigher because it is synchronized with the high-frequency deflection ofelectron beams. A limitation of breakdown voltage of transistors ofdynamic voltage driver circuits of the monitor set can not provide asufficiently high dynamic voltage to the color cathode ray tube of arequired waveform.

[0079] Considering the capability of the presently used dynamic focuscircuit, the practical dynamic voltage dVf needs to be limited to 650volts or a lower voltage.

[0080] For a color cathode ray tube employing a 1000 deflection yoke 8,of the first embodiment, to limit the dynamic voltage dVf to 650 voltsor a lower voltage, the following relationship is derived from the line“a” in FIG. 2A,

[0081] {B−20A/(3φ)}≦22.0 mm.

[0082] Incidentally, for the above-mentioned color cathode ray tubeemploying a 100° deflection yoke, previously proposed by the presentinventors, to limit the dynamic voltage dVf to 650 volts or a lowervoltage, the following relationship is derived from the line “b” in FIG.2A,

[0083] {B−20A/(3φ)}≦19.0 mm.

[0084]FIG. 2B shows that, in both the color cathode ray tubes with the,DF type in-line electron gun employing the dark-tainted panel and thetainted panel, respectively, the diameters of the electron beam spots onthe phosphor screen at the standard electron beam current is increasedwith decrease in the effective length of the final focus electrodenormalized by the lens-screen distance.

[0085] High resolution display capability is required for a colorcathode ray tube in a high-definition display monitor for use in graphicterminals or the like capable of displaying a high-resolution image ofdrawings as well as letters or characters.

[0086] Therefore, for a color cathode ray tube having a useful diagonalphosphor screen dimension of 41 cm (17 inches) or more, it is desirablethat a pith of dot-like electron beam apertures in its shadow mask is0.28 mm or less, and the number of display dots in a horizontaldirection on the phosphor screen is at least 1000, and this requires thediameter of electron beam spot at the center of the phosphor screen tobe 0.5 mm or less.

[0087] For a color cathode ray tube employing the dark-tainted panel, ofthe first embodiment, to limit the diameter of the electron beam spot onthe phosphor screen to 0.5 mm or a smaller value, the followingrelationship is derived from the line “a” in FIG. 2B,

[0088] 0.0625≦{B−20A/(3φ)}/L,

[0089] that is, 0.0625L (mm)≦B−20A/(3φ) (mm).

[0090] Incidentally, for the above-mentioned color cathode ray tubeemploying the tainted panel, previously proposed by the presentinventors, to limit the diameter of the electron beam spot on thephosphor screen to 0.5 mm or a smaller value, the following relationshipis derived from the line “b” in FIG. 2B,

[0091] 0.06≦(B−20A/(3φ)}/L,

[0092] that is, 0.06L (mm)≦B−20A/(3φ) (mm).

[0093] Color cathode ray tubes for use in monitors for informationterminals and the like are required to have a large number of pictureelements and to produce a high information content and large capacitydisplay, and therefore it is desirable that dot aperture pitches in ashadow mask is not larger than 0.28 mm and the number of display dots ina horizontal direction on the phosphor screen is at least 1000 for auseful diagonal phosphor screen dimension not smaller than 41 cm (17inches).

[0094] For ease of use of the information terminal display monitor on anordinary office desk with a space sufficient for a keyboard and thelike, the monitor needs to be made compact by making its depth as smallas possible, and therefore it is desirable to make its useful diagonalscreen dimension 51 cm (21 inches) and below.

[0095] In prior art cathode ray tubes having the maximum diagonaldeflection angle of 90°, the lens-screen distances L are about 293 mm,about 326 mm, and about 355 mm for useful diagonal screen dimensions of41 cm (17 inches), 46 cm (19 inches) and 51 cm (21 inches),respectively, and the ratio D/L of the diagonal screen dimension D tothe lens-screen distance L is smaller than 1.45.

[0096] In cathode ray tubes having the maximum diagonal deflection angleof 1000 to which the present invention is directed, the lens-screendistances L are about 258 mm, about 282 mm and about 314 mm for usefuldiagonal screen dimensions of 41 cm (17 inches), 46 cm (19 inches) and51 cm (21 inches), respectively, and the ratio D/L of the diagonalscreen dimension D to the lens-screen distance L is about 1.60.

[0097] The above values of the lens-screen distances L are selected suchthat interference of magnetic deflection fields leaking from thedeflection yoke does not distort the shape of electron beam spots on thephosphor screen beyond an allowable limit and the anode-side end of thefocus sub-electrode which forms a final stage of a main lens incooperation with the anode is disposed as close to the phosphor screenas possible.

[0098] Although color cathode ray tubes having a maximum diagonaldeflection angle of approximately 110° have been used for color TVreceivers, it is difficult to employ a color cathode ray tube having themaximum deflection angle of approximately 110 deflection in aninformation terminal display requiring a dynamic focusing circuit for ahigh information content, large capacity and high resolution displaybecause of the magnitude of the dynamic focus voltage limited bycapacity of the circuit.

[0099] The color cathode ray tube of the present invention adopts amaximum diagonal deflection angle larger than 90° in order to make itsaxial length (an overall length) shorter than that of a conventionalcolor cathode ray tube having a maximum diagonal deflection angle of90°, while still keeping the maximum diagonal deflection angle less than110° to reduce the magnitude of the dynamic voltage of the dynamic focuscircuit in the information terminal display monitor. In this colorcathode ray tube having a maximum diagonal deflection angle larger than90°, but smaller than 110°, the ratio D/L of the diagonal phosphorscreen dimension D to the lens-screen distance L is selected to be in arange of about 1.45 to about 1.70 such that the overall axial length ofthe cathode ray tube is made as short as possible, but such that themain lens of the electron gun is free from adverse effects ofinterference with leakage magnetic fields from the deflection yoke.

[0100] The range of 241 mm to 352 mm for the lens-screen distance Lcorresponds to the useful diagonal screen dimension of 41 cm (17 inches)to 51 cm (21 inches) of color cathode ray tubes.

[0101] In conclusion, the color cathode ray tube of the first embodimentcan reduce the diameter of the electron beam spot on the phosphor screento 0.5 mm or a smaller value by satisfying the following relationshipseven when the cathode ray tube employs a dark-tainted panel for thefaceplate of the panel portion and a deflection yoke 8 for a relativelylarge deflection angle, 100°, for example,

[0102] 0.0625L (mm)≦B−20A/(3φ)≦22.0 (mm), and L≦352 (mm).

[0103]FIG. 3 is a horizontal cross-sectional view of a second embodimentof a color cathode ray tube in accordance with the present invention.

[0104] In the DF type in-line electron gun 37 of FIG. 3, referencenumeral 10, denotes a left-hand cathode, 10 ₂ is a center cathode, 10 ₃is a right-hand cathode, 11 is the G1 electrode, 12 is the G2 electrode,33(1) is a first G3 sub-electrode, 33(2) is a second G3 sub-electrode,33(3) is a third G3 sub-electrode, 34 is the G4 electrode, 17 is theshield cup, 18 are the vertical electrode pieces and 19 are thehorizontal electrode pieces.

[0105] The same reference numerals as utilized in FIG. 1 designatecorresponding portions in FIG. 3.

[0106] The structure of the color cathode ray tube in the secondembodiment may be substantially the same as in the first embodiment,except that, in the second embodiment, the means for focusing theelectron beams from the electron generating means comprising thecathodes 10 ₁, 10 ₂, 10 ₃, the G1 electrode 11 and the G2 electrode 12comprises the G3 sub-electrode 33(1), 33(2), 33(3), 33(4) and the G4electrode 34.

[0107] The first to third G3 sub-electrodes 33(1) to 33(3), and the G4electrode 34 in the second embodiment are identical in structure withthe first to third G5 sub-electrodes 15(1) to 15(3), and the G6electrode 16 in the first embodiment, respectively.

[0108] The second G3 sub-electrode 33 (2) is provided with the verticalelectrode pieces 18 sandwiching horizontally each of the three electronbeam apertures in its end facing the third G3 sub-electrode 33(3), andthe third G3 sub-electrode 33(3) is provided with a pair of thehorizontal electrode pieces 19 sandwiching vertically the three electronbeam apertures in common in its end facing the second G3 sub-electrode33 (2). The vertical electrode pieces 18 and the horizontal electrodepieces 19 form an electrostatic quadrupole lens between the second andthird G3 sub-electrodes 33 (2), 33 (3).

[0109] The G1 electrode 11 is supplied with a voltage approximatelyequal to or near zero volt, the G2 electrode 12 is supplied with arelatively low voltage Vg2 of about 400 to about 1000 volts, the secondG3 sub-electrode 33(2) is supplied with a fixed voltage Vfs of about 5kV to about 10 kV, the first G3 sub-electrode 33(1) and the third G3sub-electrode 33(3) are supplied with a focus voltage (Vfd+ dVf) whichis a fixed voltage Vfd superposed with a dynamic voltage dVf varyingwith deflection of the electron beams, and the G4 electrode 34, theshield cup 17 and the internal conductive coating 6 are supplied with anaccelerating voltage (an anode voltage) Eb.

[0110] The color cathode ray tube of this embodiment forms twocurvature-of-the-image-field correction lenses between the first andsecond G3 sub-electrodes 33(1), 33(2) and between the third G3sub-electrode 33(3) and the G4 electrode 34, and one electrostaticquadrupole lens between the second and third G3 sub-electrodes 33(2),33(3) by applying the focus voltage (Vfd+dVf) containing the dynamicvoltage dVf to the first and third G3 sub-electrodes 33(1), 33(3), andcorrects astigmatism of an electron beam spot and curvature of the imagefield.

[0111] The color cathode ray tube of the second embodiment operates inthe way similar to the first embodiment. Therefore further explanationfor the structure of the second embodiment is omitted.

[0112] In the second embodiment, the effective length of the final focuselectrode adjacent to the anode is the length designated as “c”,measured from the cathode-side end of the first G3 sub-electrode 33(1)to the phosphor-screen-side end of the third G3 sub-electrode 33(3). Thecathode-side end of the first G3 sub-electrode 33(1) faces directly theaccelerating electrode (the G2 electrode) 12 in the electron beamgenerating section, and the correction terms 20A/(3φ) considered in thefirst embodiment need not be considered in the second embodiment. Thelength “c” can be adopted for the effective length of a final focuselectrode in FIGS. 2A and 2B. In this embodiment, the lens-screendistance L is a distance from a phosphor-screen-side end of the third G3sub-electrode 33(3) to the center of the phosphor screen in FIG. 3. Inthis embodiment, it is necessary to satisfy the following relationships:

[0113] 0.0625L (mm)≦C≦22.0 mm, and L≦352 (mm).

[0114] The operation of the second embodiment is substantially the sameas that of the first embodiment already described, the advantagesprovided by the second embodiment is substantially the same as those ofthe first embodiment already described, and therefore the explanation ofthe operation and the advantages of the second embodiment are omitted.

[0115]FIG. 7 is a vertical cross-sectional view of a third embodiment ofa color cathode ray tube in accordance with the present invention.

[0116] In the DF type in-line electron gun 67, reference numeral 10 ₂denotes a center cathode, 11 is the G1 electrode, 12 is the G2electrode, 13 is the G3 electrode, 14 is the G4 electrode, 65(1) is afirst G5 sub-electrode, 65(2) is a second G5 sub-electrode, 65(3) is athird G5 sub-electrode, 65(4) is a fourth G5 sub-electrode, 16 is the G6electrode, 17 is a shield cup, 18 are vertical electrode pieces and 19are horizontal electrode pieces.

[0117]FIG. 9 is a cross-sectional view of the second G5 sub-electrode65(2) of FIG. 7 as viewed in the direction of arrows IX-IX in FIG. 7,and FIG. 10 is a cross-sectional view of the third G5 sub-electrode65(3) of FIG. 7 as viewed in the direction of arrows X-X in FIG. 7.

[0118] The second G5 sub-electrode 65(2) is provided with a pair of thehorizontal electrode pieces 19 sandwiching vertically the three electronbeam apertures 652 a, 652 b, 652 c in common in its end facing the thirdG5 sub-electrode 65(3), and the third G5 sub-electrode 65(3) is providedwith the vertical electrode pieces 18 sandwiching horizontally each ofthe three electron beam apertures 653 a, 653 b, 653 c in its end facingthe second G5 sub-electrode 65(2). The vertical electrode pieces 18 andthe horizontal electrode pieces 19 form an electrostatic quadrupole lensbetween the second and third G5 sub-electrodes 65(2), 65(3).

[0119] The major difference between the first and third embodiments isthat the vertical electrode pieces 18 and the horizontal electrodepieces 19 are interchanged.

[0120] The color cathode ray tube of the third embodiment forms threecurvature-of-the-image-field correction lenses between the first andsecond G5 sub-electrodes 65(1), 65(2), between the third and fourth G5sub-electrodes 65(3), 65(4) and between the fourth G5 sub-electrode65(4) and the G6 electrode 16, and one electrostatic quadrupole lensbetween the second and third G5 sub-electrodes 65(2), 65(3) by applyingthe focus voltage (Vfd+dVf) containing the dynamic voltage dVf to thesecond and fourth G5 sub-electrodes 65(2), 65(4), and correctsastigmatism of an electron beam spot and curvature of the image field.

[0121] The color cathode ray tube of the third embodiment operates inthe way similar to the first embodiment.

[0122]FIG. 8 is a vertical cross-sectional view of a fourth embodimentof a color cathode ray tube in accordance with the present invention.

[0123] Except for the manner in which the respective electrodes aresupplied with operating voltages, the electrodes are identical withthose in the third embodiment. In this embodiment the G5 electrode isconsidered to be divided into three sub-electrodes including a first G5sub-electrode 75(1), a second G5 sub-electrode 75(2) and a third G5sub-electrode 75(3) because the first and second G5 sub-electrodes65(1), 65(2) which are electrically isolated in the third embodiment aresupplied with the same voltage Vfd in the fourth embodiment.

[0124] The color cathode ray tube of the fourth embodiment formscurvature-of-the-image-field correction lenses between the second andthird G5 sub-electrodes 75(2), 75(3) and between the third G5sub-electrode 75(3) and the G6 electrode 16, and one electrostaticquadrupole lens between the first and second G5 sub-electrodes 75(1),75(2) by applying the focus voltage (Vfd+dVf) containing the dynamicvoltage dVf to the first and second G5 sub-electrodes 15(1), 75(2), andcorrects astigmatism of an electron beam spot and curvature of the imagefield.

[0125] The color cathode ray tube of the fourth embodiment operates inthe way similar to the first embodiment.

[0126] As described above, the present invention provides the advantagesof limiting the diameter of the electron beam spot on the phosphorscreen to 0.5 mm or less, limiting the dynamic voltage to 650 volts orless and reducing appearance of raster moire even when a faceplatehaving a reduced light transmission and a wide-angle deflection yoke areemployed, by forming a lens for correcting curvature of the image fieldand an electrostatic quadrupole lens with the final focus electrodeadjacent to the anode and optimizing the length of the final focuselectrode.

[0127] The number of the sub-electrodes into which a focus electrodeadjacent to an anode is divided is three in the first, second and fourthembodiments, and four in the third embodiment, but the number of thesub-electrodes is not limited to these, and it depends upon the desirednumber of electrostatic quadrupole lenses and lens for correction ofcurvature of the image field. The electron gun of the present inventionincludes at least one of each of an electrostatic-quadrupole lens and alens for correction of curvature of the image field.

What is claimed is:
 1. A color cathode ray tube comprising: an evacuatedenvelope including a panel portion, a neck portion, a funnel portion forconnecting said panel portion and said neck portion; a phosphor screenformed on an inner surface of a faceplate of said panel portion; anin-line type electron gun housed in said neck portion; and a deflectionyoke mounted around said funnel portion; said in-line type electron guncomprising: an electron beam generating section having three in-linecathodes, a G1 electrode and a G2 electrode arranged in the order namedfor projecting three electron beams arranged approximately in parallelwith each other in a horizontal plane toward said phosphor screen; andan electron beam focusing section comprising a G3 electrode, a G4electrode, a G5 electrode and an anode arranged in the order named forfocusing said three electron beams on said phosphor screen; wherein saidG5 electrode comprises a plurality of sub-electrodes arranged to besupplied alternately with a first focus voltage and a second focusvoltage, said first focus voltage being a first fixed voltage, saidsecond focus voltage being a second fixed voltage superposed with adynamic voltage varying with deflection of said three electron beams; atleast one electrostatic quadrupole lens is formed between two of saidplurality of sub-electrodes supplied alternately with said first focusvoltage and said second focus voltage, two of said plurality ofsub-electrodes are supplied with said second focus voltage; and said G4electrode, said G5 electrode and said phosphor screen satisfy thefollowing inequalities: 0.0625×L (mm)≦B−20A/(3φ)≦22.0 mm, and L (mm)≦352mm where A (mm) is an axial length of said G4 electrode, φ (mm) is anaverage of horizontal and vertical diameters of an electron-beamaperture for a center electron beam of said three electron beams in saidG4 electrode, B (mm) is an axial length measured from a cathode side endof said G5 electrode to a phosphor screen side end of said G5 electrode,and L (mm) is an axial distance from said phosphor screen side end ofsaid G5 electrode to a center of said phosphor screen.
 2. A colorcathode ray tube according to claim 1 , wherein said second-focusvoltage is supplied to a group of said plurality of sub-electrodesincluding one nearest said anode.
 3. A color cathode ray tube accordingto claim 1 , wherein said deflection yoke is of the type having bothhorizontal and vertical deflection windings wound in a saddleconfiguration for a diagonal deflection angle in a range of 95° to 105°.4. A color cathode ray tube according to claim 1 , wherein said at leastone electrostatic quadrupole lens is formed between second and thirdones of said plurality of sub-electrodes counting from a side of saidcathode.
 5. A color cathode ray tube according to claim 1 , wherein saidplurality of sub-electrodes are at least three in number.
 6. A colorcathode ray tube according to claim 1 , wherein said plurality ofsub-electrodes are four in number.
 7. A color cathode ray tube accordingto claim 1 , wherein said first fixed voltage and said second fixedvoltage are in a range of about 5 kV to about 10 kV, and said anode issupplied with a voltage in a range of about 20 kV to about 30 kV.
 8. Acolor cathode ray tube according to claim 1 , wherein a lighttransmission of said faceplate is about 38%.
 9. A color cathode ray tubeaccording to claim 1 , further comprising a shadow mask closely spacedfrom said phosphor screen within said panel portion, wherein a pitch ofdot-like electron beam apertures in said shadow mask is 0.28 mm or less.10. A color cathode ray tube comprising: an evacuated envelope includinga panel portion, a neck portion, a funnel portion for connecting saidpanel portion and said neck portion; a phosphor screen formed on aninner surface of a faceplate of said panel portion; an in-line typeelectron gun housed in said neck portion; and a deflection yoke mountedaround said funnel portion; said in-line type electron gun comprising:an electron beam generating section having three in-line cathodes, a G1electrode and a G2 electrode arranged in the order named for projectingthree electron beams arranged approximately in parallel with each otherin a horizontal plane toward said phosphor screen; and an electron beamfocusing section comprising a G3 electrode, and an anode arranged in theorder named for focusing said three electron beams on said phosphorscreen; wherein said G3 electrode comprises a plurality ofsub-electrodes arranged to be supplied alternately with a first focusvoltage and a second focus voltage, said first focus voltage being afirst fixed voltage, said second focus voltage being a second fixedvoltage superposed with a dynamic voltage varying with deflection ofsaid three electron beams; at least one electrostatic quadrupole lens isformed between two of said plurality of sub-electrodes suppliedalternately with said first focus voltage and said second focus voltage,two of said plurality of sub-electrodes are supplied with said secondfocus voltage; and said G3 electrode and said phosphor screen satisfythe following inequalities: 0.0625×LA (mm)≦C≦22.0 mm, and L (mm)≦352 mmwhere C (mm) is an axial length measured from a cathode side end of saidG3 electrode to a phosphor screen side end of said G4 electrode, and LA(mm) is an axial distance from said phosphor screen side end of said G3electrode to a center of said phosphor screen.
 11. A color cathode raytube according to claim 10 , wherein said second focus voltage issupplied to a group of said plurality of sub-electrodes including onenearest said anode.
 12. A color cathode ray tube according to claim 10 ,wherein said deflection yoke is of the type having both horizontal andvertical deflection windings wound in a saddle configuration for adiagonal deflection angle in a range of 95° to 105°.
 13. A color cathoderay tube according to claim 10 , wherein said at least one electrostaticquadrupole lens is formed between second and third ones of saidplurality of sub-electrodes counting from a side of said cathode.
 14. Acolor cathode ray tube according to claim 10 , wherein said plurality ofsub-electrodes are at least three in number.
 15. A color cathode raytube according to claim 10 , wherein said plurality of sub-electrodesare four in number.
 16. A color cathode ray tube according to claim 10 ,wherein said first fixed voltage and said second fixed voltage are in arange of about 5 kV to about 10 kV, and said anode is supplied with avoltage in a range of about 20 kV to about 30 kV.
 17. A color cathoderay tube according to claim 10 , wherein a light transmission of saidfaceplate is about 38%.
 18. A color cathode ray tube according to claim10 , further comprising a shadow mask closely spaced from said phosphorscreen within said panel portion, wherein a pitch of dot-like electronbeam apertures in said shadow mask is 0.28 mm or less.